Question

Camera A has a lens with an aperture
diameterof 8.40. It photographs an object using the correctexposure
time of 3.33×10−2.What exposure time should be used with camera B
inphotographing the same object with the same film if this camera
hasa lens with an aperture diameter of 23.1? The lenses of cameras A and B have the same
focallength.

I tried to find the intensity by
23.1/8.4....then *the time... but then i got so wrong.. any
help??